Many gas-solid reactions an performed in circulating fluidized beds which are either operated in the downer or riser mode. Good gas-solid contact in the early stages of the reaction is crucial to such reactors. A simple experimental tool has been developed for rapid, rough characterization of the gas-solids dispersion at the mixing chamber exit. A simplified momentum probe provides instantaneous pressure signals at seven radial locations. Cross-correlation analysis of these signals results in three new indices : a mixing index, a uniformity index and a stability index. These indices have been successfully applied to the selection of the best mixing chamber for a downer.